1. Field of the Invention
Devices, systems, and methods consistent with the invention are related to routing in a mobile ad-hoc network, and more particularly, to routing in a mobile ad-hoc network that allows each node in a network to: measure a packet transmission rate using a signal-to-noise ratio (SNR) to its neighboring node, measure a variation in the number of neighboring nodes due to their insertion or deletion; distribute a relative packet transmission time relative to the SNR, which is measured using the packet transmission rate; and determine a routing path using the stored relative packet transmission time relative to the SNR.
2. Description of the Related Art
With the drastic advancement of computer technologies and wireless communication technologies, improved mobile wireless computers using Internet Protocol (IP) communication are expected to gain increasing popularity. In the wake of this trend, mobile ad-hoc networks are emerging to support robust and efficient operation. These mobile ad-hoc networks have multi-hop topologies which are composed of relatively bandwidth-constrained wireless links.
To enable communication between any two nodes in a mobile ad-hoc network environment, a data packet must be routed through multiple hops between the two nodes.
Routing for packet switching in a mobile ad-hoc network environment consisting of mobile nodes connected by wireless links differs from routing in a wired environment in that a dynamic network topology variation frequently occurs and the quality of a link between nodes varies continuously in time and space domains.
FIG. 1 illustrates a related art connection between nodes.
The goal of a mobile ad-hoc network is to extend mobility of a node. A node is connected to a router and another node, thereby forming a network routing infrastructure in an ad-hoc fashion.
When an ad-hoc network is formed as shown in FIG. 1, a node A can send a packet to another node (e.g., B-J) along a path determined according to a routing table, such as is shown in FIG. 2.
FIG. 2 shows a routing table for the node A shown in FIG. 1, which is stored at the node A. Using this routing table, the node A selects a path with the minimum number of hops, from the stored paths, and sends a data packet according to the selected path.
An improved approach to this method is to first select a path by calculating a packet delivery rate or a packet error rate, and then send a data packet according to the selected path. The packet delivery rate or the packet error rate represents a ratio of the number of packets broadcast by every node in a network during a given period to the number of data packets normally received by each node from its neighboring nodes for a given period. Each node has a table storing packet delivery rates or packet error rates for all nodes, and can determine link quality using such a table to send a data packet.
Accordingly, there are two types of related art data packet routing methods between wireless nodes: (1) a routing method using the number of hops; and (2) a routing method using a packet delivery rate or a packet error rate.
However, the related art routing methods have drawbacks in that variations in link quality in the time and space domains cannot be reflected in the routing. For example, the routing method using the number of hops cannot guarantee link quality because a network environment varies with time and space. Further, the routing method using a packet delivery rate or a packet error rate presents a problem of inaccuracy when a node moves because the packet delivery rate or the packet error rate obtained by measuring the number of packets received from neighboring nodes for a certain period varies depending on the relative position of the node.
A further issue to be considered in the related art routing methods is illustrated in FIG. 3, which shows asymmetric communications performed when each node has a different wireless communication radius. In FIG. 3, node A 310, node B 320, node C 330, and node D 340 have different network radii. Here, since the node A 310 and the node C 330 lie within the radius of each other, it is possible to exchange data between the node A 310 and the node C 330. However, while the node B 320 is within the radius of the node A 310, the node A 310 is not within the radius of node B 320. Thus, the node A 310 can recognize the existence of the node B 320 and can send data to the node B 320, but the node B 320 cannot recognize the existence of the node A 310 and cannot send data to the node A.
Since a link between nodes is asymmetric due to multi-path fading and external interference in an actual mobile ad-hoc network environment, this property of the link should also be reflected in a routing method.